Anatase crystals of unusual habit in quartz veins from the Diamantina region (Espinhaço Range, Minas Gerais)

Professor, Universidade Federal de Minas Gerais - UFMG, Instituto de Geociências, Belo Horizonte - Minas Gerais - Brasil. mlschaves@gmail.comUniversidade Federal de Minas GeraisBrazilBelo Horizonte, Minas Gerais, BrazilProfessor, Universidade Federal de Minas Gerais - UFMG, Instituto de Geociências, Belo Horizonte - Minas Gerais - Brasil. mlschaves@gmail.com

Joachim Karfunkel

Professor, Universidade Federal de Minas Gerais - UFMG, Instituto de Geociências, Belo Horizonte - Minas Gerais - Brasil. jkarfunkel@yahoo.comUniversidade Federal de Minas GeraisBrazilBelo Horizonte, Minas Gerais, BrazilProfessor, Universidade Federal de Minas Gerais - UFMG, Instituto de Geociências, Belo Horizonte - Minas Gerais - Brasil. jkarfunkel@yahoo.com

Vladimir Bermanec

University of Zagreb, Institute of Mineralogy and Petrology, Hortovac bb 10000 - Zagreb - Croatia. vberman@public.carnet.hrUniversity of ZagrebCroatiaZagreb, CroatiaUniversity of Zagreb, Institute of Mineralogy and Petrology, Hortovac bb 10000 - Zagreb - Croatia. vberman@public.carnet.hr

Vladimir Zebec

Croatian Natural History Museum, Demetrova - Zagreb - Croatia. vladimir.zebec@pfos.hrCroatian Natural History MuseumCroatiaDemetrova, Zagreb, CroatiaCroatian Natural History Museum, Demetrova - Zagreb - Croatia. vladimir.zebec@pfos.hr

Ricardo Scholz

Professor, Universidade Federal de Ouro Preto - UFMG, Escola de Minas, Ouro Preto - Minas Gerais - Brasil. r_scholz_br@yahoo.comUniversidade Federal de Ouro PretoBrazilOuro Preto, Minas Gerais, BrazilProfessor, Universidade Federal de Ouro Preto - UFMG, Escola de Minas, Ouro Preto - Minas Gerais - Brasil. r_scholz_br@yahoo.com

Luiz Alberto D. Menezes Filho
(In Memoriam)

(In Memoriam)

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (9)
Tables (1)

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Figure 1
(a). General geologic map of the southern Espinhaço Range, with the arrow showing the focused area south of the Diamantina town in Minas Gerais State (MG). (b). Geologic map of the Datas-Gouveia region with the locations of the two studied Datas de Cima and Caxambu anatase deposits (modified from Fogaça, 1996FOGAÇA, A. C. C. Mapa Geológico da Folha Diamantina, Minas Gerais. Belo Horizonte: Convênio COMIG/IGC-UFMG, 1996. (1 mapa).).

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Figure 2
(a). Panoramic view of the diamond exploration area north of Datas town showing the old Datas de Cima diamond mine (red arrow points toward the location of the anatase depo sit). (b). View of the mined quartz vein.

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Figure 3
(a). Panoramic view of the Caxambu farm area (Gouveia County), showing a flattened area where Basal Complex rocks outcrop, surrounded by quartzite hills of the Espinhaço Supergroup (red arrow marks the location of the anatase deposit). (b). Detail of one of the shafts cutting argillaceous schists in which the deposit is located. (c). Irregular quartz vein about 20 cm wide with negative prints of the anatase crystals. (d). Detail of one of these 1.5 cm cavity.

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Figure 4
(a). Parcel of "common" form of gray-bluish anatase crystals found in diamond-bearing alluvial placers from the Jequitinhonha River (Diamantina). (b). Detail of a quartz specimen also with a "common" form of brown-yellowish anatase crystal on quartz from other local in the Datas region.

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Figure 5
(a). Typical anatase crystals showing double bipyramidal forms from the Datas de Cima deposit. (b). A more elongated crystal from this deposit, showing different forms in its central part.

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Figure 6
Idealized drawing of slightly different anatase crystallographic models of the second type from Datas de Cima deposit (case (a) represents the crystal from Figure 5b).

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Figure 7
(a) Anatase crystal with parallel growths. (b) A possible idealized drawing for these aggregates.

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Figure 8
(a). Anatase crystal partially coated by rutile from Caxambu farm. (b). Anatase crystal coated by two stacks of rutile needles (left) and with a "near-commom" form, without rutile coat (right). (c). Anatase crystal completely coated by rutile.

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Figure 9
(a). Anatase crystal half coated by rutile. (b). Anatase crystal coated by rutile except on the two apexes, where pure anatase still remains; some tiny quartz crystals also occur (c/d). Complex forms of anatase crystals intensely coated by rutile.

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Table 1
Electron microprobe analyses in representative samples of yellow-golden crystals of anatase from Caxambu deposit, Gouveia (G-1 to G-4), and gray-bluish crystals from Jequitinhonha River, Diamantina (J-1 to J-4) (means of five spots; all iron content as Fe²⁺; Nd, not determined). Literature comparisons: RC-a and RC-b, Rio Cipó, Diamantina region; CL, Capão do Lana topaz mine, Ouro Preto; D-un, unknown locality in Diamantina region (Deer et al., 1962DEER, W. A. et alii. Rock-forming minerals, London: Longman, 1962, (v. 5 - Non-silicates). 371 p.).

Figure 1 (a). General geologic map of the southern Espinhaço Range, with the arrow showing the focused area south of the Diamantina town in Minas Gerais State (MG). (b). Geologic map of the Datas-Gouveia region with the locations of the two studied Datas de Cima and Caxambu anatase deposits (modified from Fogaça, 1996FOGAÇA, A. C. C. Mapa Geológico da Folha Diamantina, Minas Gerais. Belo Horizonte: Convênio COMIG/IGC-UFMG, 1996. (1 mapa).).

Figure 2 (a). Panoramic view of the diamond exploration area north of Datas town showing the old Datas de Cima diamond mine (red arrow points toward the location of the anatase depo sit). (b). View of the mined quartz vein.

Figure 3 (a). Panoramic view of the Caxambu farm area (Gouveia County), showing a flattened area where Basal Complex rocks outcrop, surrounded by quartzite hills of the Espinhaço Supergroup (red arrow marks the location of the anatase deposit). (b). Detail of one of the shafts cutting argillaceous schists in which the deposit is located. (c). Irregular quartz vein about 20 cm wide with negative prints of the anatase crystals. (d). Detail of one of these 1.5 cm cavity.

Figure 4 (a). Parcel of "common" form of gray-bluish anatase crystals found in diamond-bearing alluvial placers from the Jequitinhonha River (Diamantina). (b). Detail of a quartz specimen also with a "common" form of brown-yellowish anatase crystal on quartz from other local in the Datas region.

Figure 5 (a). Typical anatase crystals showing double bipyramidal forms from the Datas de Cima deposit. (b). A more elongated crystal from this deposit, showing different forms in its central part.

Figure 6 Idealized drawing of slightly different anatase crystallographic models of the second type from Datas de Cima deposit (case (a) represents the crystal from Figure 5b).

Figure 7 (a) Anatase crystal with parallel growths. (b) A possible idealized drawing for these aggregates.

Figure 8 (a). Anatase crystal partially coated by rutile from Caxambu farm. (b). Anatase crystal coated by two stacks of rutile needles (left) and with a "near-commom" form, without rutile coat (right). (c). Anatase crystal completely coated by rutile.

Figure 9 (a). Anatase crystal half coated by rutile. (b). Anatase crystal coated by rutile except on the two apexes, where pure anatase still remains; some tiny quartz crystals also occur (c/d). Complex forms of anatase crystals intensely coated by rutile.

Table 1 Electron microprobe analyses in representative samples of yellow-golden crystals of anatase from Caxambu deposit, Gouveia (G-1 to G-4), and gray-bluish crystals from Jequitinhonha River, Diamantina (J-1 to J-4) (means of five spots; all iron content as Fe²⁺; Nd, not determined). Literature comparisons: RC-a and RC-b, Rio Cipó, Diamantina region; CL, Capão do Lana topaz mine, Ouro Preto; D-un, unknown locality in Diamantina region (**Deer et al., 1962**DEER, W. A. et alii. Rock-forming minerals, London: Longman, 1962, (v. 5 - Non-silicates). 371 p.).

No.	TiO₂	FeO	Al₂O₃	V₂O₅	SnO₂	PF	Total
G-1	99.68	0.67	Nd	Nd	Nd	Nd	100.35
G-2	98.86	1.17	Nd	Nd	Nd	Nd	100.03
G-3	98.49	0.93	Nd	Nd	Nd	Nd	99.42
G-4	98.45	1.21	Nd	Nd	Nd	Nd	99.66
J-1	99.66	0.08	Nd	Nd	Nd	Nd	99.74
J-2	99.93	0.11	Nd	Nd	Nd	Nd	100.04
J-3	99.78	0.13	Nd	Nd	Nd	Nd	99.91
J-4	99.81	0.14	Nd	Nd	Nd	Nd	99.95
RC-a	98.98	0.15	0.15	0.00	0.00	0.77	100.15
RC-b	98.86	0.00	0.00	0.86	0.00	0.53	100.25
CL	98.60	1.40	0.00	0.00	0.00	0.00	100.00
D-un	98.36	1.11	0.00	0.00	0.20	0.00	99.67

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Anatase crystals of unusual habit in quartz veins from the Diamantina region (Espinhaço Range, Minas Gerais)

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[1] (In Memoriam)